Process for producing carbonized fibrous products

ABSTRACT

Carbonized textile products having both improved tensile strength and modulus of elasticity properties are produced by heating a cellulosic textile substrate until a first carbonized textile product of at least 50 percent by weight carbon is produced and exposing the carbonized textile product to further heating while applying tension to the product until a second carbonized product having a carbon content of between 60-100 percent by weight carbon is produced.

United States Patent Ross 1 1 May 16, 1972 54] PROCESS FOR PRODUCING 3,412,062 11/1968 Johnson et a1. ....23/209.1 x CARBONIZED FIBROUS PRODUCTS 3,449,077 6/ 1969 Stuetz ..23/209.1 3,454,362 7/1969 Spry ....23/209.1 [72] Inventor: Stanley E. Ross, Passaic, NJ- 3,529,934 9/1970 Shindo ..23/209.1 [73] Assignee: J. P. Stevens 8: Co., Inc., New York, N.Y 3,540,848 11/1970 Krugler et a1. ..23/209.1 X [22] Filed: May 31, 1968 OTHER PUBLICATIONS [21] App]. No.: 733,516 Schmidt et a1; Chem. Eng. Progress Vol. 58, No. 10, Oct.

[52] US. Cl ..23/Z09.4, 8/116, 23/209. 1 primary Examiner Edwa-d J Mel-OS 264/29 Attorney-Michae1 T. Frimer and Bernard Marlowe [51] Int. Cl. ..C01b 31/07 [58] Field of Search ..23/209.4, 209.2, 209.1; 57 ABSTRACT Carbomzed textile products having both improved tensile 56] References Cited strength and modulus of elasticity properties are produced by heating a cellulosic textile substrate until a first carbonlzed UNITED STATES PATENTS textile product of at least 50 percent by weight carbon is produced and exposing the carbonized textile product to 2913302 l 1959 further heating while applying tension to the product until a L98] 12/1961 second carbonized product having a carbon content of 3,04 1 6/1962 between 60-100 percent by weight carbon is produced. 3,235,323 2/1966 3,294,489 12/ 1966 Millington et a1 ..23/209.4 4 Claims, 3 Drawing Figures PATENTEDHAY 16 I972 Q. 3 D g g WINDUP mvsmon STANLEY E. Ross MMM V ATTORNEY PROCESS FOR PRODUCING CARBONIZED FIBROUS PRODUCTS This invention concerns the preparation of carbonized textile products having both improved tensile strength and modulus of elasticity properties.

More particularly, this invention relates to a carbonization process whereby tension is applied to partially carbonized cel lulosic textile substrates during heat treatment to produce strengthened more fully carbonized products.

The term tension" as used throughout this application is a generic term including all means of applying stress to a cellulosic substrate. This term includes stretching, using draw rolls operating at different rates of speed, the application of weights, the use of gears and the like.

The term carbonization refers to a process whereby substrates containing less than 45 percent carbon are thermally transformed to carbonized products containing from 50-100 percent by weight carbon.

The term partially carbonized refers to cellulosic substrates such as yarns, fibers, filaments, cloths and the like whose carbon content varies between about 50 percent up to about 85 percent by weight carbon. The more fully carbonized products are those in which the carbon content varies between about 85-100 percent by weight carbon.

To aid in the understanding of this invention the three accompanying figures are submitted.

FIGS. 1, 2 and 3 represent flow sheets relating to different embodiments of the inventive process described in detail in the specification below.

The use of carbonized products for electrical and aerospace applications offers numerous advantages including lightness, chemical inertness, dimensional stability and good resistance to flammability and high temperature ablation. Carbonized structures are advantageous compared to graphitized structures in that they are less costly, are less dense, have higher surface areas and are better electrical and thermal insulators. Because of their lower thermal conductivity the carbonized structures also have superior cold side shielding properties. Partially graphitized structures suffer from the same disadvantages only to a lesser degree.

One serious drawback of carbonized structures has been their relatively poor tensile strength and modulus properties. This has limited their end use to rather special applications such as aerospace hardware. The published procedures for preparing carbonized products from cellulosic substrates such as the rayons involves the lengthy stepwise heating of the substrate at lower temperatures (usually 250 to 500 C.) followed by a rather brief heating conducted at about l,300 to 2,700 C. Higher temperatures produce graphitization and are to be avoided. These processes which can involve treatment of the cellulosic substrates with various catalysts and heating in an inert environment are illustrated by U.S. Pat. Nos. 3,235,323 (Peters); 3,294,489 (Millington et al.); and 3,305,315 (Bacon et al.). However, whatever the process variations employed, all of the disclosed processes produce a product containing up to 95 percent by weight carbon content which, while otherwise satisfactory, has relatively poor tensile strength, poor modulus of elasticity, and for certain end uses leave something to be desired. A very recent Belgian Patent, No. 700,655 which is said to produce a carbonized product which has greatly improved strength and modulus properties uses the more expensive substrate polyacrylonitrile. In addition, the process applies tension during the initial carbonization stage which is inapplicable to cellulosics. A significant advance in the art would be represented by a process which would permit upgrading the strength properties of products obtained through carbonizing the economical and readily available cellulosic substrates utilizing existing techniques and equipment.

Therefore, it is the general object of this invention, among others, to substantially improve the tensile strength and modulus properties of carbonized products utilizing the inexpensive and readily available cellulosic substrates, techniques and apparatus.

More specific objects are the production of carbon products having many of the desirable attributes of graphite without some of the undesirable characteristics of graphite; said products being produced by a less costly process conducted at substantially lower temperatures than are required for graphitization and without the more specialized equipment required for graphitization.

Additional objects will suggest themselves to those skilled in,

the art after a perusal of this specification including the flow sheets illustrating the preferred process embodiments of this invention.

In practice, the above objects are achieved by applying tension to a cellulosic substrate while it is exposed to carbonizing temperatures until a carbonized product containing between about 60-100 percent by weight carbon is obtained.

In one favored process a cellulosic substrate is heated between about 200 to 300 C. to produce a carbonized intermediate having a carbon content of from about 50 to 60 percent by weight carbon. The carbonized intermediate is exposed to temperatures ranging from about 500 to l,000 C., while a first tension is applied to the heated material. The heating is continued until a carbon content of from about 70-85 percent by weight carbon is obtained. Finally, the above material is heated between about l,000 to 1,500" C. for a time sufficient to produce a product having up to percent by weight carbon, substantially free from graphite as demonstrated by X-ray diffraction patterns.

In the preferred process embodiment, a rayon yarn substrate is treated with one or more of the compositions described infra and designated as catalyst, in l-l0 percent by weight concentration until a pickup of -300 percent by weight on the substrate is achieved. The treated yarn is dried to a moisture content of approximately 8-12 percent and is first heated at 200-300 C. During this heating no tension is applied to the yarn and the yarn is allowed to shrink freely. This lack of tensioning during the initial carbonization is necessary because the cellulosic substrates unlike other carbon-containing substrates such as polyacrylonitrile, are greatly weakened during this heating stage due to the complex molecular changes which have taken place. Therefore, it should be emphasized that the tensioning cannot be performed during the initial carbonization between 200 and 300 C. and is confined to the subsequent carbonization of the 50 percent by weight carbon yarn materials produced from the initial carbonization. The product obtained is a fibrous material having a carbon content between about 50-60 percent by weight carbon.

The first carbonized yarn product is then heated a second time between about 500 C. to about l,000 C. in a non-oxidizing atmosphere while a first tension is applied to the yarn. The tension applied is less than the amount required to break the yarn, and the heating is continued until a second carbonized yarn having a carbon content between about 70-85 percent by weight carbon is produced. This carbon yarn can then be wound for future use. Alternatively, this carbon yarn product is heated a third time between about 1,000 to 1,500" C. in a non-oxidizing atmosphere such as nitrogen, helium and argon or their mixtures with or without air, while a second tension is applied to the yarn. Heating is continued until a third carbonized product having a carbon content between about 85-100 percent by weight carbon is produced.

To aid in an understanding of the inventive process some of the more salient details of the inventive process are described below:

1. Cellulosic Substrates The cellulosic substrates of this invention are limited to the cellulosics of natural and synthetic origin. The cellulosics are preferred substrates because of their high carbon content, good initial strength, lower cost and the good quality of the resultant carbonized product. The preferred cellulosic substrates are the regenerated celluloses or rayons but cotton, linen, hemp, jute, flax, sisal and the like can be used of convenient. These substrates are preferably in the form of their yarn but can be in the form of staple, fibers, continuous filament tows, cloths (woven, knitted or felted), non-woven, random layed fibrous or needle-punched batts, felts, fabrics or tissue, laminates and the like.

2. Carbonization Catalysts While the process of this invention does not require them, the use of carbonization catalysts is preferred as they reduce carbonization time and appear to give products possessing optimum physical properties. Any of the carbonization catalysts previously described in the literature can be employed, particularly diammonium hydrogen phosphate, phosphorothioic triamide, N,N' ,N' -trimethylphosphoric triamide, phosphonitrile amide cyclic trimer, phosphoric triamide, diethyl methylphosphoramidate, methylphosphonic diamide, (chloromethyl)phosphonothionic diamide, trimethyl phosphate, triethyl phosphate, diethyl ethylphosphoramidate and diethyl isopropylphosphoramidate, among many others.

3. Carbonization Temperatures and Carbonization Periods The carbonization can be conducted stepwise or continuously through the range of 2501,500 C. The temperature employed depends upon the carbon content desired. At the 50-60 percent by weight carbon level, temperatures between about 200300 C. will suffice whereas to obtain products of 85-95 percent by weight carbon, temperatures in excess of 1,000 C. are required. In the latter case the upper temperature must not go above about l,500 C. or unwanted graphitization with its attendant disadvantages takes place. As indicated earlier, excellent results have been obtained utilizing a three-step heating cycle. In the first step no tension is applied during heating at 200-300 C. A tensioning step takes place when the carbonization takes place between about 500-l, 000 C. At the end of these two heating stages a product having a carbon content between about 70-85 percent by weight carbon is obtained whereas to obtain a product above 85 percent by weight carbon or higher, a final heating about 1,000 C. and up to l,500 C. is required.

The carbonization periods are variable and depend upon the carbonization catalysts and carbonization temperatures employed. However, ordinarily within the framework of the three heating steps described above, the initial heating step require a total of under 1 hour, ordinarily under 30 minutes, whereas the heating between 1,000 and 1,500 C. is very brief, usually under a minute or two.

4. Application of Tension The application of tension to a cellulosic substrate which has been previously carbonized to a carbon-containing intermediate having a carbon content of at least 50 percent by weight carbon is the gist of this invention. As indicated earlier, the tension can be applied in one or more separate operations dependent upon the equipment available and the convenience of the party. The tension need not be applied by one method generally speaking it can be applied by any known means of applying stress to the cellulosic substrate as it undergoes carbonization. These include deadweight techniques (the application of weights to the substrate), the use of draw rolls traveling at different rates of speed and the like.

The amount of tension required for producing a noticeable improvement in the strength properties of the carbonized product is a variable dependent upon several factors, and therefore cannot be stated with precision. Primarily, the tension is dependent upon the number of distinct heating stages employed and the temperatures at which these stages operate. Generally, the tension required ranges between the tension required to exceed the natural shrinkage (5-20 percent of original dimensions) that the substrate undergoes during carbonization up to just under the tension required to exert a breaking stress on the substrate. A convenient way of expressing the tension required is by load per denier. Expressed in this manner the minimum tension that can be effectively applied is of the order of about 0.03 gram/denier of substrate whereas the upper limit as measured by breaking stress is ordinarily in the order of about 0.60 gram/denier. When a threestage heating cycle is used to produce'a carbonized yarn,

generally a tension of about 0.04 to 0.30 gram/denier is applied in the second stage at a tension of about 0.05 to 0.40 gram/denier is applied in the third stage. In a typical threestage heating cyclewhere the first stage is maintained at 260 C., the second at 550 C. and the third at 1,400 C., wherein the tension is applied during the second and third heating, the tensions will ordinarily range between about 50-150 grams per LOGO-1,200 denier of substrate for the second heating stage and between about 50-200 grams per 650-850 denier of substrate for the third heating stage.

At the end of the second heating stage the carbonized product has a carbon content ranging between about 70-85 percent by weight carbon. This product is then briefly heated carefully up to no higher than 1,500 C. to raise the carbon content to about -95 percent by weight carbon without forming substantial amounts of undesirable graphite.

Having described the inventive process generally, it only remains to disclose specific embodiments of the process. A description of the techniques used to determine tensile strength and modulus of elasticity of the carbonized yarn and the method used to apply the tension, precede the examples.

TENSILE STRENGTH A suitable length of the aforedescribed cellulosic yarn which has been carbonized is taken for sampling. Samples of the 50-60 percent by weight, 70-85 percent by weight, and 85-100 percent by weight carbon yarn are used. All samples are conditioned for 16 hours at 65 percent RH. and 21 C. The sample is tested on an lnstron Tensile Tester (manufactured by Instron Engineering Corp.) as follows: Thesamples are positioned so that the span between the jaws of the instrument are 1 inch, and in some instances 5 inches. An appropriate load cell is used. The rate of extension is 10 percent per minute and the chart speed adjusted so that every inch on MODULUS OF ELASTICITY The modulus of elasticity expressed in grams per denier is determined from the slope of the stress-strain curve obtained in the tensile strength determination.

FIGS. 1 to 3 in the drawing describe three embodiments of the process of the instant invention.

FIG. 1 shows the preferred 2 (two)-tensioning-3(three)- heating stage embodiment of this invention. In the drawing a cellulosic substrate 1 is treated with catalyst solution C. The substrate travels in a left to right direction at a pre-selected rate of speed as it enters the first furnace 2 maintained between about '200-300 C. where the first carbonization to about 50 to 60 percent by weight carbon content takes place. The partially carbonized yarn leaves the furnace, passes through a pair of nip-rolls 3 over a set of guide means 5, while being exposed to a first tensioning step applied by means of a tension arm 4. After passing over the set of guide means 5 the substrate passes into a second furnace 6 maintained at between about 500 to 1,000 C. to produce a second carbonized product of higher carbon (about 70-85 percent by weight) content. This second carbonized product leaves the second furnace, passes through a second set of nip rolls 7 over guide means 9, has a second tension applied to it through a second tension arm 8 and passes over second set of guide means 9 into the third furnace 10 maintained between about 1,000 to I,500 C. to produce a more fully carbonized product having a carbon content of between about 85-100 percent by weight carbon. This product is taken up or otherwise gathered and stored for further treatment or use.

FIG. 2 illustrates a l(one)-tensioning-3(three)-heating stage process. In the figure the substrate 21 is treated with catalyst solution C and travels from left to right at a preselected rate of speed to enter the first furnace 22 maintained at about 200 to 300 C. until a first carbonized product of about 50-60 percent by weight carbon is produced. Again, as in FIG. 1, the partially carbonized substrate exits and passes between a first pair of nip-rolls 23 and guide means 25 while a first tension is applied to it by means of a tension arm 24. After passing over guide means 25 the substrate enters a second furnace 26 maintained at about 500 to 1,000 C. until the second EXAMPLE 1 APPLICATION OF ONE TENSIONING STEP TO A PARTIALLY CARBONIZED RAYON YARN SUBSTRATE EXPOSED TO THREE HEATING ZONES carbonization to a carbon content of about 70-85 percent by 5 In this example rayon yarn substrate 1,650 denier, 720 filaweigh car n takes place The mg, more l y r mz ments) is treated with phosphoric triamide and carbonized as product passes between a second pair of nip-rolls 27 into the shown in table 1, below: I TABLE 1 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, C. T1, g. 2, C. Tr, g. 3, C g./denier g./denier (a) 260 None 011 None 1, 375 2. 4 116 (b) .1 260 None 538 None 1, 375 Z. 5 118 (c) 260 60 538 None 1, 375 z. s 134 (d) 260 100 538 None 1, 375 3. 1 176 NOTE.-AII products have at least 110% by weight carbon.

third furnace 28 maintained between about l,000 and 1,500 C. where the final carbonization to a product of about 85-100 percent by weight carbon content takes place. Again, this product is taken up" or wound up upon an appropriate storage means. Where a partially carbonized product is desired the procedure shown in FIG. 2 is followed except that the third furnace 28 is dispensed with.

FIG. 3 shows a variation of the l(one)-tensioning-3(three)- heating step process of FIG. 2. In this variation, the substrate 3 treated with catalyst solution C travels from left to right at a rate of speed required to give the desired residence time in the furnaces, enters the first furnace 32 maintained at about 200 to 300 C. and exits as a carbonized product having a carbon content between about 50-60 percent by weight carbon. This partially carbonized substrate passes between a first set of niprolls 33 from which it is drawn into the second carbonizing furnace 34, maintained at about 500 to 1,000 C. to produce a second more fully carbonized product having a carbon content of between about 70-85 percent by weight carbon. The second carbonized product passes through a second set of nip- EXAMPLE 2 APPLICATION OF ONE TENSIONING STEP AFTER THE EXPOSURE OF A PARTIALLY CARBONIZED RAYON YARN SUBSTRATE TO A SECOND HEATING ZONE.

EXAMPLE 3 APPLICATION OF ONE AND TWO TENSIONING STEPS TO A PARTIALLY CARBONIZED RAYON YARN SUBSTRATE EXPOSED TO THREE HEATING ZONES In this example the same substrate and catalyst employed in example 1 are used. Experimental conditions are shown in table 2 below:

TABLE 2 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, C. Tr, g. 2, 0. T g. 3, C gJdenier g./denier 260 None 05 None 1, 375 2. 4 116 260 None 760 None 1, 375 2. 2 103 189 260 60 760 None 1, 375 3. 1 14!] 260 100 760 None 1, 375 3. 2 180 269 260 100 760 150 1, 375 3. 4 214 H. 260 100 760 200 1, 375 3. 4 202 332 Tested at 5-inch gage length.

Norm-All products have at least 90% by weight carbon.

rolls 35 and guide means 37 at which time the first and only tension is applied to the material by means of a tension arm 36. The material under tension passes over guide means 37 on its route to the third furnace 38 maintained at about 1,000 to l,500 C. Again, a more fully carbonized product having a carbon content between about 85-100 percent by weight carbon is produced and removed for subsequent end use. Where desired a comparable fully carbonized product such as is produced by the process of FIG. 3 can be obtained by following the procedure shown in FIG. 3, but eliminating the intermediate furnace F To set forth the instant process in the greatest possible EXAMPLE 4 APPLICATION OF ONE AND TWO TENSIONING STEPS TO A PARTIALLY CARBONIZED RAYON YARN SUBSTRATE EXPOSED TO THREE HEATING ZONES detail, the following examples are submitted:

TABLE 3 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, (1 T 5:. 2, (1. '1-, g. 3, gJdenier gJdenier (1 206 None 760 None 1, 375 .2. 8 180 (h) 265 30 7150 None l, 376 3. 3 244 (u) 265 30 760 1'20 1, 375 3. X .388

Norm. -All products have at least by weight ern'lron.

EXAMPLE trimethylphosphoric triamide, phosphonitrile amide cyclic trimer, methylphosphonic diamide, APPLICATION OF ONE TENSIONING STEP To A (chloromethyl )phosphonothionic diamide, trimethyl PARTIALLY CARBONIZED RAYON YARN EXPOSED phosphate, methyl phosphate diethyl To THREE HEATXNG ZONES 5 methylphosphoramidate, diethyl ethylphosphoramidate, In this example the same substrate and catalyst used in exdiethyl isopropylphosphoramidate and diammonium ample l are employed. Experimental conditions are shown in h h Th properties f h fi l products are comParathe a l below! ble to those obtained in example 7.

TABLE 4 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, C. T;, g. 2, C. T g. 3, C. g./denier g./dcniei' (a) 260 None 0ft None 1, 375 2. 4 l is (b) 260 871 Nelle 1, 375 3. 1 174 (c) 260 871 None 1, 375 3. l 181 (d) .260 100 871 N one 1, 375 3. 3 210 NOTE.-AII products have at least by weight carbon. m 7

EXAMPLE 6 2o EXAMPLE 9 APPLICATION OF ONE TENSIONING STEP TO A PARTIALLY CARBONIZED RAYON YARN EXPOSED TO TWO HEATING ZONES In this example the substrate of example l is used. Samples 25 a) to (c) have phosphoric triamide catalyst applied to them, while samples (d) to (f) utilize phosphonitrile amide cyclic trimer. Table 5 below, lists the experimental conditions used.

THE USE OF DIFFERENT CARBONIZATION I CATALYSTS IN THE TWO TENSIONING THREE- HEATING ZONE PROCESS OF EXAMPLE 3 The two-tensioning step procedure of example 3 is followed except that the following additional catalysts are employed: phospherothioic triamide, phosphoric triamide, N,N,N"

TABLE 5 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, 0. Ti, g 2, 0. T2, g. 3, C g./danler gJdenicr 260 None 816 None Off 0. 48 107 .260 811) None Cd 0. 89 137 260 140 y 816 None Of! 1. 12 171 260 None 927 None Ofi 0. 23 93 260 50 027 None Off 0. 57 172 260 70 927 None Off 0. 61 188 *Testod at 5-inch gage length. Norm-All products have 70-80% by weight carbon.

EXAMPLE? trimethylphosphoric triamide, phosphonitrile amide cyclic trimer, methylphosphonic diamide,

APPLICATION OF ONE TENSIONING STEP To A 4 (chloromethyl)phosphonothionic diamide, I trimethyl PARTIALLY CARBONIZED RAYON SUBSTRATE phosphate m h l phosphate, diethyl EXPOSED To Two HEATING ZONES methylphosphoramidate, diethyl ethylphosphoramidate,

In this example the substrate of example 6 is employed. diethyl isopropylphosphoramidate and diammonium Samples (a) to (c) utilize phosphoric triamide as catalyst. 50 hydrogen phosphate. Again comparable products are ob- Samples ((1) and (e) utilize phosphononitrile amide cyclic tained.

trimer. In all instances a single tensioning step is used. Table 6 summarizes the experimental conditions used.

TABLE 6 Properties Process conditions Tensile Furnace Furnace Furnace strength, Modulus, 1, 0. T1, g. 2, 0. T g. 3, C. gJdenier gJdenier 260 None Ofi None 1, 375 2. 4 118 260 None Off 50 1, 375 2. 6 136 260 None Ofi I00 I, 375 2. 8 I55 260 None Off None 1, 375 *2. 4 179 260 None Off 1, 375 "T2. 7 348 *Tcstcd nt 5-inch gage length. N o'rE.All products have at least 90% by weight carbon.

EXAMPLE 8 THE USE OF DIFFERENT CARBONIZATION CATALYSTS IN THE ONE-TENSIONING TWO-HEATING ZONE PROCESS OF EXAMPLE 7 EXAMPLE I0 70 APPLYING THE PROCESS DISCLOSED IN BELGIAN PAT. NO. 700,755 TO APPLICANTS CELLULOSIC SUBSTRATE Belgian PAT. No. 700,655 discloses that strengthened carbonized fibers can be obtained by applying tension to a polyacrylonitrile fiber substrate during its initial carbonization at temperatures ranging from about 220 to 250 C. The carbonization is carried out in an oxidizing atmosphere. In order to determine whether the process of the Belgium patent which is performed on a non-cellulosic substrate (polyacrylonitrile),

is applicable to applicant's cellulosic substrate (rayon) the following experiment is undertaken.

The rayon yarn substrate of example 1, is exposed to an oxidizing atmosphere at a temperature of 240 C. during carbonization. During this time, as specified by the Belgian Patent, sufficient tension is applied to the yarn to prevent it from shrinking. After a short period of time the yarn ruptures causing the experiment to be terminated. Upon repeating the experiment the same yarn failure is encountered during approximately the same reaction time.

The above experiment indicates that the process of the above Belgian Patent is not applicable to applicants cellulosic substrate.

As the preceding examples indicate, several advantages, both in the process and product evolve from the practice of this invention. For example, the carbonized yarn products of this invention have greatly improved tensile strength and modulus of elasticity compared to carbonized yarns of the prior art. Further, the gain in strength and modulus properties is achieved without the substantial presence of graphite. As has been disclosed earlier for certain end uses, carbonized products are advantageous to the corresponding graphitized structures.

The process aspects of this invention are both advantageous and unexpected. It is much less costly to produce carbonized products (as opposed to graphitized products) because the process can operate at substantially lower temperatures using more simple furnaces. It was unexpected that a substantial percentage of the gain in strength and modulus properties could be achieved at substantially lower heating temperatures without the presence of any sizeable amount of graphite in the product.

Additional advantages will suggest themselves to those skilled in the art after reading this application.

As the specification, including examples, attests numerous modifications and changes can be made in reactants, catalysts and reaction conditions without departing from the inventive concept. For example, a variety of different cellulosic textile substrates can be employed, a variety of carbonization catalysts can be used and the heating and tensioning can be applied in one or more steps as long as no tensioning takes place during the initial carbonization carried out between 200 to 300 C., when the substrate is in a weakened condition. The metes and bounds of this invention are best shown by the claims which follow:

What is claimed is:

l. process for preparing a carbonized textile product comprising:

a. heating a cellulosic textile substrate at a temperature of from about 200 to 300 C. while permitting said substrate to shrink freely until a first carbonized product is produced having a carbon content of from about 50 to 60 percent by weight and b. heating said first carbonized product at a temperature of from about 500 to 1,000 C. in a non-oxidizing atmosphere while applying tension thereto until a second carbonized product is obtained having a carbon content of from about 70 to percent by weight, said tension ranging from that required to exceed the shrinkage forces in the first carbonized product during heating, up to but less than the tension required to exert a breaking stres on the first carbonized product during heating.

2. A process as claimed in claim 1 including the additional step of heating said second carbonized product at a temperature of from about 1,000 to l,500 C. in a non-oxidizing atmosphere while applying tension thereto until a third carbonized product is obtained having a carbon content of from about 85 to percent by weight, said tension ranging from that required to exceed the shrinkage forces in the second carbonized product during heating, up to but less than the tension required to exert a breaking stress on the second carbonized product during heating.

3. A process for preparing a carbonized textile product comprising:

a. heating a cellulosic textile substrate at a temperature of from about 200 to 300 C. while permitting said substrate to shrink freely until a first carbonized product is produced having a carbon content of from about 50 to 60 percent by weight and b. heating said first carbonized product at a temperature of from about 500 to 1,500" C. in a non-oxidizing atmosphere while applying tension thereto until a second carbonized product is obtained having a carbon content of from about 70 to 100 percent by weight, said tension ranging from that required to exceed the shrinkage forces in the first carbonized product during heating, up to but less than the tension required to exert a breaking stress on the first carbonized product during heating and said temperature being at least 1,000 C. when the carbon content of said second carbonized product is greater than 85 percent by weight.

4. A process for preparing a carbonized yarn comprising:

a. subjecting a cellulosic yarn to a first heat treatment at a temperature of from about 200 to 300 C. while permitting said yarn to shrink freely until a partially carbonized yarn is produced having a carbon content of from about 50 to 60 percent by weight, and

b. subjecting said partially carbonized yarn to a heat treatment at a temperature of from about 500 to l,500 C. in a non-oxidizing atmosphere while maintaining said yarn under a tension of from about 0.03 to 0.60 gram/denier until a carbonized yarn is obtained having a carbon content of from about 70 to 100 percent by weight, provided that a temperature of at least 1,000" C. is used to obtain a carbon content greater than 85 percent by weight. 

2. A process as claimed in claim 1 including the additional step of heating said second carbonized product at a temperature of from about 1,000* to 1,500* C. in a non-oxidizing atmosphere while applying tension thereto until a third carbonized product is obtained having a carbon content of from about 85 to 100 percent by weight, said tension ranging from that required to exceed the shrinkage forces in the second carbonized product during heating, up to but less than the tension required to exert a breaking stress on the second carbonized product during heating.
 3. A process for preparing a carbonized textile product comprising: a. heating a cellulosic textile substrate at a temperature of from about 200* to 300* C. while permitting said substrate to shrink freely until a first carbonized product is produced having a carbon content of from about 50 to 60 percent by weight and b. heating said first carbonized product at a temperature of from about 500* to 1,500* C. in a non-oxidizing atmosphere while applying tension thereto until a second carbonized product is obtained having a carbon content of from about 70 to 100 percent by weight, said tension ranging from that required to exceed the shrinkage forces in the first carbonized product during heating, up to but less than the tension required to exert a breaking stress on the first carbonized product during heating and said temperature being at least 1,000* C. when the carbon content of said second carbonized product is greater than 85 percent by weight.
 4. A process for preparing a carbonized yarn comprising: a. subjecting a cellulosic yarn to a first heat treatment at a temperature of from about 200* to 300* C. while permitting said yarn to shrink freely until a partially carbonized yarn is produced having a carbon content of from about 50 to 60 percent by weight, and b. subjecting said partially carbonized yarn to a heat treatment at a temperature of from about 500* to 1,500* C. in a non-oxidizing atmosphere whIle maintaining said yarn under a tension of from about 0.03 to 0.60 gram/denier until a carbonized yarn is obtained having a carbon content of from about 70 to 100 percent by weight, provided that a temperature of at least 1,000* C. is used to obtain a carbon content greater than 85 percent by weight. 